Prepreg, metal foil-clad laminate, and printed wiring board

ABSTRACT

A prepreg having low water absorption, and having remarkably suppressed deterioration in insulation resistance over time, and further having excellent heat resistance, a metal foil-clad laminate using the prepreg, and a printed wiring board using the metal foil-clad laminate are provided. A prepreg of the present invention is obtained by impregnating or coating a base material (D) with a resin composition comprising: a naphthol-modified dimethylnaphthalene formaldehyde resin (A); an epoxy resin (B) having an epoxy equivalent of 200 to 400 g/eq.; and an inorganic filler (C).

TECHNICAL FIELD

The present invention relates to a prepreg, a metal foil-clad laminateusing the prepreg, and a printed wiring board.

BACKGROUND ART

In recent years, there are increasingly accelerated high integration andminiaturization of semiconductors widely used in electronic equipment,communication instruments, personal computers or the like. This demandsvarious better characteristics of laminates for semiconductor plasticpackages.

Conventionally, as the laminates used in the semiconductor plasticpackages, a prepreg and a metal foil-clad laminate obtained byimpregnating or coating a base material with a resin compositioncontaining an epoxy resin and a curing agent are widely known. Further,various curing agents such as amines, acid anhydrides, and phenols areknown.

Phenolic resins are used as the curing agent of the resin compositionfor the laminate for semiconductor plastic package. Among them,phenol-based resins having a small number of hydroxyl groups withrespect to a molecular weight are known as the phenolic resins havinglow water-absorption properties. For example, a biphenylaralkyl-basedphenolic resin, a naphthol aralkyl-based phenolic resin, and anovolac-based phenolic resin obtained by reacting a naphthaleneformaldehyde resin with phenols or the like are known as thephenol-based resins having low water-absorption properties (for example,see Patent Literatures 1 to 5).

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 2004-123859-   Patent Literature 2: Japanese Patent Laid-Open No. 2009-001812-   Patent Literature 3: Japanese Patent Laid-Open No. 2009-108147-   Patent Literature 4: International Publication No. WO 03/055927-   Patent Literature 5: Japanese Patent Laid-Open No. 2009-155638

SUMMARY OF INVENTION Technical Problem

In recent years, the reduction in the water absorption of the laminatefor the semiconductor plastic package has been strongly desired. This isbecause a decrease in insulation resistance which may be generated whenthe laminate absorbs water, and insulation failure such as ion migrationare easily caused by the miniaturization of a circuit. However, theconventional phenolic resin used as the curing agent is merely used forthe purpose of mainly improving the flame retardancy of a curedmaterial. The phenolic resin is not sufficiently considered from theviewpoint of a reduction in water absorption in a prepreg, a printedwiring board or the like, which is a resin composition or a curedmaterial thereof.

The present invention has been made in view of the above problems. It isan object of the present invention to provide a prepreg having low waterabsorption, and of which deterioration in insulation resistance overtime is remarkably suppressed, a metal foil-clad laminate using theprepreg, and a printed wiring board using the metal foil-clad laminate.It is another object of the present invention to provide a prepreghaving low water absorption, and of which deterioration in insulationresistance over time is remarkably suppressed, and further havingexcellent heat resistance, a metal foil-clad laminate using the prepreg,and a printed wiring board using the metal foil-clad laminate.

Solution to Problem

The present inventors have diligently studied in order to solve theproblems. As a result, the inventors found that the problems are solvedby using a resin composition containing a specific naphthol-modifieddimethylnaphthalene formaldehyde resin (A), an epoxy resin (B) having anepoxy equivalent of 200 to 400 g/eq., and an inorganic filler (C). Thepresent invention has been attained.

That is, the present invention provides the following [1] to [8].

[1]

A prepreg obtained by impregnating or coating a base material (D) with aresin composition containing:

a naphthol-modified dimethylnaphthalene formaldehyde resin (A);

an epoxy resin (B) having an epoxy equivalent of 200 to 400 g/eq.; and

an inorganic filler (C), wherein the naphthol-modifieddimethylnaphthalene formaldehyde resin (A) is obtained by condensing adimethylnaphthalene formaldehyde resin and (c) a naphthol compoundrepresented by the following general formula (1) in the presence of anacidic catalyst,

wherein R₁ and R₂ each independently represent a hydrogen atom or analkyl group having 1 to 3 carbon atoms, and

the dimethylnaphthalene formaldehyde resin obtained by condensing (a) atleast one dimethylnaphthalene selected from the group consisting of1,5-dimethylnaphthalene, 1,6-dimethylnaphthalene,2,6-dimethylnaphthalene, 1,7-dimethylnaphthalene,1,8-dimethylnaphthalene, and 2,7-dimethylnaphthalene and (b)formaldehyde in the presence of an acidic catalyst.

[2]

The prepreg according to [1], wherein the epoxy resin (B) is abiphenylaralkyl-based epoxy resin.

[3]

The prepreg according to [1] or [2], wherein a hydroxyl equivalent ofthe naphthol-modified dimethylnaphthalene formaldehyde resin (A) is 300to 600 g/eq.

[4]

The prepreg according to any one of [1] to [3], wherein the inorganicfiller (C) is silica.

[5]

The prepreg according to any one of [1] to [4], wherein a content of thenaphthol-modified dimethylnaphthalene formaldehyde resin (A) is 40 to 70parts by mass based on 100 parts by mass in total of the (A) ingredientand the (B) ingredient.

[6]

The prepreg according to any one of [1] to [5], wherein a content of theinorganic filler (C) is 5 to 300 parts by mass based on 100 parts bymass in total of the (A) ingredient and the (B) ingredient.

[7]

A metal foil-clad laminate using the prepreg according to any one of [1]to [6].

[8]

A printed wiring board using the metal foil-clad laminate according to[7].

Advantageous Effects of Invention

The present invention can simply achieve a prepreg having low waterabsorption, and of which deterioration in insulation resistance overtime is remarkably suppressed, with good reproducibility. Furthermore,the present invention can also achieve a prepreg having heat resistanceequivalent to that of a conventional product. Therefore, by using theprepreg, the present invention can easily achieve a metal foil-cladlaminate and a printed wiring board which have low water absorption andremarkably improved temporal stability of insulation resistance whilehaving heat resistance equivalent to that of the conventional product.As a result, the reliability of a product is improved.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described.The following embodiment is illustrative in order to describe thepresent invention. The present invention is not limited only to theembodiment.

A prepreg of the present embodiment is obtained by impregnating orcoating a base material (D) with a resin composition containing: aspecific naphthol-modified dimethylnaphthalene formaldehyde resin (A);an epoxy resin (B) having an epoxy equivalent of 200 to 400 g/eq.; andan inorganic filler (C).

The naphthol-modified dimethylnaphthalene formaldehyde resin (A) usedherein is obtained by condensing a dimethylnaphthalene formaldehyderesin and (c) a naphthol compound represented by the following generalformula (1) in the presence of an acidic catalyst. Thedimethylnaphthalene formaldehyde resin is obtained by condensing (a) atleast one dimethylnaphthalene selected from the group consisting of1,5-dimethylnaphthalene, 1,6-dimethylnaphthalene,2,6-dimethylnaphthalene, 1,7-dimethylnaphthalene,1,8-dimethylnaphthalene, and 2,7-dimethylnaphthalene and (b)formaldehyde in the presence of an acidic catalyst:

wherein R₁ and R₂ each independently represent a hydrogen atom or analkyl group having 1 to 3 carbon atoms.

As the formaldehyde used in the above-mentioned condensation reactionwith the dimethylnaphthalene, compounds capable of generatingformaldehyde such as formalin, paraformaldehyde and trioxan and thelike, all of which are industrially easily available can be utilized.Herein, the compounding amount of the dimethylnaphthalene and theformaldehyde when performing the condensation reaction is notparticularly limited. However, from the viewpoint of increasing yield, amolar ratio of the dimethylnaphthalene to the formaldehyde is preferably1:1 to 1:6, more preferably 1:2 to 1:6, and still more preferably 1:2.5to 1:5. Examples of the acidic catalyst used in the condensationreaction of the dimethylnaphthalene and the formaldehyde include, butare not particularly limited to, sulfuric acid. The condensationreaction can also be performed in the presence of water and an acidiccatalyst if necessary.

The synthesis condition of the dimethylnaphthalene formaldehyde resinmay be performed by properly applying a known technique withoutparticular limitation. For example 1,5-dimethylnaphthalene, a formalinaqueous solution, and concentrated sulfuric acid are placed in areaction vessel, and are reacted by stirring while refluxing uponheating in a nitrogen gas stream. Then, the reactant is neutralized byan acid, and is extracted by an organic solvent. Thereby, a1,5-dimethylnaphthalene formaldehyde resin can be obtained.

Specific examples of an alkyl group having 1 to 3 carbon atoms in (c)the naphthol compound used in the naphthol modification of thedimethylnaphthalene formaldehyde resin and represented by generalformula (1) include a methyl group, an ethyl group, an n-propyl group,and an isopropyl group. Furthermore, in (c) the naphthol compoundrepresented by general formula (1), each of R₁ and R₂ is preferably ahydrogen atom. More specifically, (c) the naphthol compound representedby general formula (1) is more preferably 1-naphthol or 2-naphthol.

Examples of the acidic catalyst used in the naphthol modification of thedimethylnaphthalene formaldehyde resin include, but are not particularlylimited to, sulfuric acid and p-toluenesulfonic acid. Among them, thep-toluenesulfonic acid is preferable.

Other synthesis condition in the naphthol modification of thedimethylnaphthalene formaldehyde resin can be performed by properlyapplying a known technique without particular limitation. For example,the dimethylnaphthalene formaldehyde resin and (c) the naphthol compoundrepresented by general formula (1) are refluxed upon heating in thepresence of the acidic catalyst, and thereby the naphthol-modifieddimethylnaphthalene formaldehyde resin (A) can be obtained. Although thecondensation reaction is usually performed at atmospheric pressure, thecondensation reaction may also be performed under an elevated pressureif necessary. Furthermore, a solvent which is inert to the condensationreaction can be used if necessary. Examples of the solvent includearomatic hydrocarbons such as toluene, ethylbenzene, and xylene;saturated aliphatic hydrocarbons such as heptane and hexane; alicyclichydrocarbons such as cyclohexane; ketones such as methyl isobutylketone; ethers such as dioxane and dibutyl ether; alcohols such as2-propanol; carboxylic acid esters such as ethyl propionate; andcarboxylic acids such as acetic acid. A heating temperature in thepresence of the acidic catalyst is not particularly limited. However,from the viewpoint of the high viscosity of the resin, the heatingtemperature is preferably 100 to 250° C., more preferably 120 to 200°C., and still more preferably 150 to 200° C. Inactive gases such asnitrogen, helium, argon, and water vapor may be passed in a reactionsystem. A general method may be employed, which if necessary, furtheradds the solvent for dilution after the end of the reaction, allows themixture to stand to cause two-phase separation, separates a resin phaseas an oily phase from an aqueous phase, further washes it with water,thereby completely removing the acidic catalyst, and then removes theadded solvent and the unreacted naphthol compound by distillation, orthe like.

The naphthol-modified dimethylnaphthalene formaldehyde resin (A)obtained as described above preferably has a hydroxyl equivalent of 300to 600 g/eq. without particular limitation. A prepreg having low waterabsorption and having heat resistance equivalent to that of theconventional product tends to be easily obtained by using thenaphthol-modified dimethylnaphthalene formaldehyde resin (A) having ahydroxyl equivalent made to fall within this range. The hydroxylequivalent of the naphthol-modified dimethylnaphthalene formaldehyderesin (A) can be adjusted by the compounding ratio of thedimethylnaphthalene formaldehyde resin and the naphthol compound in thenaphthol modification.

The content of the naphthol-modified dimethylnaphthalene formaldehyderesin (A) may be properly set according to desired properties withoutparticular limitation. From the viewpoint of the water absorption of theobtained prepreg or the like, the content of the naphthol-modifieddimethylnaphthalene formaldehyde resin (A) is preferably 40 to 70 partsby mass based on 100 parts by mass in total of the naphthol-modifieddimethylnaphthalene formaldehyde resin (A) and the epoxy resin (B). Thenaphthol-modified dimethylnaphthalene formaldehyde resins (A) may beused singly or in combinations of two or more.

By contrast, a known epoxy resin, for example, an epoxy resin used as amaterial for a printed wiring board may be properly used as the epoxyresin (B) having an epoxy equivalent of 200 to 400 g/eq. used in thepresent embodiment as long as the epoxy equivalent satisfies the range.The kind thereof is not particularly limited. Specific examples thereofinclude biphenylaralkyl-based epoxy resins, bisphenol A-based epoxyresins, bisphenol E-based epoxy resins, bisphenol F-based epoxy resins,bisphenol S-based epoxy resins, phenol novolac-based epoxy resins,cresol novolac-based epoxy resins, bisphenol A novolac-based epoxyresins, trifunctional phenol-based epoxy resins, tetrafunctionalphenol-based epoxy resins, naphthalene-based epoxy resins,biphenyl-based epoxy resins, aralkyl novolac-based epoxy resins,alicyclic epoxy resins, polyol-based epoxy resins, glycidyl ester-basedepoxy resins, phenolaralkyl-based epoxy resins, aralkyl novolac-basedepoxy resins, biphenylaralkyl-based epoxy resins, naphtholaralkyl-basedepoxy resins, dicyclopentadiene-based epoxy resins, polyol-based epoxyresins, glycidylamines, glycidyl esters, compounds obtained byepoxidizing a double bond of butadiene and the like, and compoundsobtained by reacting hydroxyl-containing silicone resins withepichlorohydrin or halides thereof. These may be used singly or incombinations of two or more. Among them, from the viewpoint of flameretardancy, heat resistance and the like when the epoxy resin (B) andthe naphthol-modified dimethylnaphthalene formaldehyde resin (A) areused in combination, the epoxy resin (B) is preferably thebiphenylaralkyl-based epoxy resin. Especially, an epoxy resinrepresented by the following formula (2) is particularly preferable:

wherein n represents an integer of 1 or more.

From the viewpoint of realizing the prepreg having low water absorption,or the like, the epoxy equivalent of the epoxy resin (B) needs to be 200to 400 g/eq. From the viewpoint of the water absorption of the obtainedprepreg or the like, the epoxy equivalent is more preferably 250 to 350g/eq.

The content of the epoxy resin (B) may be properly set according todesired properties without particular limitation. From the viewpoint ofthe water absorption and the heat resistance of the obtained prepreg orthe like, the content of the epoxy resin (B) is preferably 30 to 60parts by mass based on 100 parts by mass in total of thenaphthol-modified dimethylnaphthalene formaldehyde resin (A) and theepoxy resin (B).

An inorganic filler known in the art may be properly selected and usedas the inorganic filler (C) used in the present embodiment withoutparticular limitation. Specific examples thereof include, but are notparticularly limited to, silicas such as natural silica, syntheticsilica, fused silica, amorphous silica, and hollow silica, boehmite,molybdenum compounds such as molybdenum oxide and zinc molybdate, zincborate, zinc stannate, alumina, zinc oxide, magnesium oxide, zirconiumoxide, aluminium hydroxide, boron nitride, clay, kaolin, talc, calcinedclay, calcined kaolin, calcined talc, mica, glass short fibers(including fine powders of glasses such as E-glass, T-glass, D-glass,S-glass, and Q-glass), hollow glass, and spherical glass. These may beused singly or in combinations of two or more. Among them, from theviewpoint of characteristics of a laminate such as a low coefficient ofthermal expansion, the silicas are preferably used as the inorganicfiller (C).

The content of the inorganic filler (C) may be properly set according todesired properties without particular limitation. From viewpoint of thecharacteristics of the laminate such as the low coefficient of thermalexpansion of the obtained prepreg or the like, the handleability uponmanufacturing, and the impregnatability into a glass cloth, the contentof the inorganic filler (C) is preferably 5 to 300 parts by mass basedon 100 parts by mass in total of the naphthol-modifieddimethylnaphthalene formaldehyde resin (A) and the epoxy resin (B), andmore preferably 150 to 300 parts by mass.

The prepreg of the present embodiment can be obtained by impregnating orcoating a base material (D) with a resin composition containing the (A)ingredient to the (C) ingredient. Herein, the resin composition maycontain a silane coupling agent and a wet dispersing agent in such anamount that does not sacrifice desired characteristics of the resincomposition. The dispersibility of the inorganic filler in the resincomposition can be improved by incorporating the silane coupling agentor the wet dispersing agent.

Any silane coupling agent commonly used for surface treatment ofinorganic materials may be suitably used without particular limitation.Specific examples thereof include, but are not particularly limited to,aminosilane coupling agents such as γ-aminopropyltriethoxysilane andN-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, epoxysilane couplingagents such as γ-glycidoxypropyltrimethoxysilane, vinylsilane couplingagents such as γ-methacryloxypropyltrimethoxysilane, cationic silanecoupling agents such asN-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilanehydrochloride, and phenylsilane coupling agents. These may be usedsingly or in combinations of two or more.

Any dispersion stabilizer used for coating materials may be suitablyused as the wet dispersing agent without particular limitation.Especially, the wet dispersing agent is preferably a polymer wetdispersing agent having an acid group(s), and more preferably a polymerwet dispersing agent having an acid value of 20 to 200 mgKOH/g. Specificexamples thereof include, but are not particularly limited to, polymerwet dispersing agents manufactured by BYK Japan K.K. such asDisperbyk-110, Disperbyk-111, Disperbyk-180, BYK-161, BYK-W996,BYK-W9010, BYK-W903, and BYK-W940. These may be used singly or incombinations of two or more.

Furthermore, the resin composition may contain curing accelerators toproperly adjust a curing speed if necessary. This type of curingaccelerator is known in the art. For example, any curing acceleratorcommonly used as curing accelerators for epoxy resins or phenolic resinsmay be suitably used. Specific examples of the curing acceleratorinclude, but are not particularly limited to, organometal salts ofcopper, zinc, cobalt, nickel or the like, imidazoles and derivativesthereof, and tertiary amines. These may be used singly or incombinations of two or more.

Furthermore, the resin composition may contain solvents if necessary.For example, by using the organic solvents are used, the viscosity ofthe resin composition when the resin composition is prepared can belowered, to improve the handleability of the resin composition and theimpregnatability of a glass cloth with the resin composition. Anysolvent may be used without particular limitation as long as the mixtureof the naphthol-modified dimethylnaphthalene formaldehyde resin (A) andthe epoxy resin (B) can be dissolved therein or is compatible therewith.Specific examples thereof include ketones such as acetone, methyl ethylketone, methyl isobutyl ketone, and cyclohexanone, aromatic hydrocarbonssuch as benzene, toluene, and xylene, amides such as dimethylformamideand dimethylacetamide, and propylene glycol methyl ether and acetatethereof. These may be used singly or in combinations of two or more.

The resin composition may contain ingredients other than those listedabove in such an amount that does not sacrifice desired characteristicsof the resin composition. Examples of the optional ingredients includevarious polymeric compounds such as heat-curable resins, thermoplasticresins, and oligomers or elastomers thereof, flame-retardant compounds,and various additives other than those listed above. Any of them whichare commonly used in the art may be used without particular limitation.Specific examples of the flame-retardant compounds includenitrogen-containing compounds such as melamine and benzoguanamine, andoxazine ring-containing compounds. Specific examples of the additivesinclude ultraviolet absorbers, antioxidants, photopolymerizationinitiators, fluorescent brighteners, photosensitizers, dyes, pigments,thickeners, lubricants, antifoaming agents, dispersants, levelingagents, brighteners, and polymerization inhibitors. These optionalingredients may be used singly or in combinations of two or more.

The resin composition can be prepared by an ordinary method. As long asthe method is a preparing method providing a resin composition uniformlycontaining the naphthol-modified dimethylnaphthalene formaldehyde resin(A), the epoxy resin (B), the inorganic filler (C), and the otheroptional ingredients, the preparing method is not particularly limited.For example, a mixture obtained by incorporating the inorganic filler(C) into the epoxy resin (B) is dispersed in a homomixer or the like.Then, the naphthol-modified dimethylnaphthalene formaldehyde resin (A)is incorporated into the mixture, and the mixture is sufficientlystirred. Thereby, the resin composition can be easily prepared. Knowntreatments (stirring, mixing, kneading treatments or the like) can beperformed to uniformly dissolve or disperse ingredients when the resincomposition is prepared. For example, in the case of the titaniumdioxide (C), stirring-dispersion treatment is performed by using astirring vessel to which a stirrer having suitable stirring capabilityis attached, to improve the dispersibility of the titanium dioxide (C)for the resin composition. The stirring, mixing, and kneading treatmentscan be properly performed by using apparatuses aiming at mixing such asa ball mill and a bead mill, or known apparatuses such as revolution androtation type mixing apparatuses. From the viewpoint of lowering theviscosity of the resin composition when the resin composition isprepared, to improve the handleability of the resin composition and theimpregnatability of the glass cloth with the resin composition, anorganic solvent is desirably added. Specific examples thereof arepreviously described.

The prepreg of the present embodiment may be obtained by combining theresin composition with a base material, specifically by impregnating orcoating the base material with the resin composition. A method forproducing the prepreg may be performed in accordance with an ordinarymethod without particular limitation. For example, the prepreg of thepresent embodiment can be produced by impregnating or coating the basematerial (D) with the resin composition (resin varnish) and thereafterheating the impregnated or coated base material in a drier of 100 to200° C. for 1 to 60 min to semi-cure (B-stage) the resin composition.The resin content (the amount of the resin composition (containing theinorganic filler) based on the total amount of the prepreg) of theprepreg is preferably 20 to 90% by mass without particular limitation.

The base material (D) used when the prepreg is produced is notparticularly limited. Known base materials used in various materials forprinted wiring boards may be properly selected and used depending uponcontemplated applications and properties. Specific examples thereofinclude glass fibers such as E-glass fibers, D-glass fibers, S-glassfibers, NE-glass fibers, T glass fibers, Q-glass fibers, and sphericalglass fibers, inorganic fibers other than the glass fibers such asquartz fibers, and organic fibers such as polyimide, polyamide, andpolyester fibers. These base materials may be properly selected and useddepending upon contemplated applications and properties. The basematerials may be used singly or in combinations of two or more. A wovencloth, a nonwoven cloth, a roving, a chopped strand mat, a surfacing matand the like are known as the shape of the base material. Plain weave,basket weave, twill weave and the like are known as a method for weavingthe woven cloth. These known products may be properly selected and useddepending upon contemplated applications and properties. Among them,products subjected to split treatment and a glass woven clothsurface-treated by using a silane coupling agent or the like aresuitably used. The thickness or mass of the base material is notparticularly limited. Usually, the base material having a thickness ofabout 0.01 to 0.3 mm is suitably used. Especially, from the viewpoint ofstrength and water-absorption properties, the base material ispreferably a glass woven cloth having a thickness of 200 μm or less anda mass of 250 g/m² or less, and more preferably a glass woven cloth madeof a glass fiber of E-glass.

On the other hand, the metal foil-clad laminate of the presentembodiment can be obtained by placing one prepreg or stacking at leasttwo prepregs, disposing a metal foil on one side or both sides of theprepreg or the stacked prepregs, and laminate-molding the metal foil andthe prepreg or the stacked prepregs. Specifically, the metal foil-cladlaminate of the present embodiment can be produced by placing oneprepreg or stacking a plurality of prepregs, disposing a metal foil madeof copper, aluminum or the like on one side or both sides of the prepregor the stacked prepregs if desired, and laminate-molding the metal foiland the prepreg or the stacked prepregs if necessary. Any metal foilused for the materials for printed wiring boards may be used hereinwithout particular limitation, and known copper foils such as a rollingcopper foil and an electrolysis copper foil are preferable. Thethickness of the metal foil is not particularly limited. The thicknessis preferably 2 to 70 μm, and more preferably 2 to 35 μm. A conditionfor molding the metal foil-clad laminate is not particularly limited.Techniques and conditions for conventional laminates for printed wiringboards and multilayered boards can be applied. For example, when themetal foil-clad laminate is molded, a multistage pressing machine, amultistage vacuum pressing machine, a continuous molding machine, anautoclave molding machine and the like can be used. The laminationmolding is generally carried out in the ranges of a temperature of 100to 300° C., a planar pressure of 2 to 100 kgf/cm², and a heating time of0.05 to 5 hr. Furthermore, postcuring may also be performed at atemperature of 150 to 300° C. if necessary. A multilayered board can beformed by lamination molding of a combination of the prepreg of thepresent embodiment with a separately produced wiring board for aninternal layer.

The metal foil-clad laminate of the present embodiment may be suitablyused as the printed wiring board by forming a predetermined wiringpattern. The printed wiring board can be produced by an ordinary methodwithout particular limitation. For example, a monolayer printed wiringboard can be produced by forming a predetermined wiring pattern on themetal foil of the metal foil-clad laminate by etching. A multilayerprinted wiring board can be produced by laminate-molding the metal foilon the printed wiring board with the prepreg sandwiched therebetween,and forming a predetermined wiring pattern on the metal foil by etching.Herein, the number of wiring layers can also be further increased bylaminate-molding metal foil on the surface with the prepreg sandwichedtherebetween and forming a predetermined wiring pattern on the metalfoil by etching. As other method, a multilayer printed wiring board canbe produced by interposing prepregs between a plurality of printedwiring boards, laminate-molding metal foils on the surface with theprepregs sandwiched therebetween, and forming a predetermined wiringpattern on the metal foils on the surface by etching. The metalfoil-clad laminate and the printed wiring board of the presentembodiment may be obtained by combining the prepreg of the presentembodiment with other prepreg (for example, an organic fiber basematerial prepreg).

EXAMPLES

Hereinafter, the present invention will be described in detail withreference to synthesis examples, Examples, and Comparative Examples.However, the present invention is not limited by these Examples in anyway. Hereinafter, unless otherwise noted, “part” represents “part bymass.”

Synthesis Example 1 Synthesis of 1,5-Dimethylnaphthalene FormaldehydeResin

In a bottom-removal four-necked flask having an internal volume of 2 Land equipped with a Dimroth condenser, a thermometer, and a stirringblade, 218 g (1.4 moles) of 1,5-dimethylnaphthalene (manufactured byMitsubishi Gas Chemical Company, Inc.), 420 g (5.6 moles asformaldehyde) of a 40% by mass formalin aqueous solution (manufacturedby Mitsubishi Gas Chemical Company, Inc.), and 194 g of 98% by masssulfuric acid (manufactured by Kanto Chemical Co., Inc.) were placed,and the mixture was stirred and reacted in a nitrogen gas stream atatmospheric pressure while refluxing at 100° C. After the reaction for 7hours, 360 g of ethylbenzene was added as a diluting solvent, and afterallowing the mixture to stand, an aqueous phase as a lower phase wasremoved. Furthermore, after neutralization and washing with water, theethylbenzene and unreacted 1,5-dimethylnaphthalene were distilled off invacuo, thereby obtaining 250 g of a 1,5-dimethylnaphthalene formaldehyderesin which is solid at normal temperature.

A weight average molecular weight (Mw) and a number average molecularweight (Mn) as reduced into polystyrene were determined by means of agel permeation chromatography (GPC) analysis, and a degree of dispersion(Mw/Mn) was determined. The resin had Mn of 550, Mw of 1,130, and Mw/Mnof 2.05.

Apparatus: Model Shodex GPC-101 (manufactured by Showa Denko K.K.)

Column: LF-804×3

Eluent: THF 1 ml/min

Temperature: 40° C.

Synthesis Example 2 Synthesis of Naphthol-Modified DimethylnaphthaleneFormaldehyde Resin

In a four-necked flask having an internal volume of 500 mL and equippedwith a Dimroth condenser, a thermometer and a stirring blade, 90 g ofthe 1,5-dimethylnaphthalene formaldehyde resin obtained in synthesisExample 1, 71.1 g (0.49 moles) of 1-naphthol, and 0.36 g ofp-toluenesulfonic acid were added in a nitrogen gas stream; thetemperature was elevated to 185° C.; and the mixture was allowed toreact for 4 hours. After diluting with ethylbenzene, neutralization andwashing with water were carried out, and removal of the solvent andunreacted 1-naphthol was carried out in vacuo, thereby obtaining 160 gof a naphthol-modified dimethylnaphthalene formaldehyde resin.

As a result of the GPC measurement in the same manner as in the abovemeasurement, the resin had Mn of 848, Mw of 1,630, and Mw/Mn of 1.93.

Example 1 Production of Prepreg

58 parts by mass of the naphthol-modified dimethylnaphthaleneformaldehyde resin (hydroxyl equivalent: 440 g/eq.) obtained insynthesis example 2, 42 parts by mass of a biphenylaralkyl-based epoxyresin (NC-3000-FH, epoxy equivalent: 320 g/eq. manufactured by NipponKayaku Co., Ltd.), 100 parts by mass of fused silica (manufactured byAdmatechs Co., Ltd.), and 0.02 part by mass of imidazole (2E4MZ,manufactured by Shikoku Chemicals Corporation) were mixed to prepare avarnish.

The varnish was diluted with methyl ethyl ketone. A 0.1 mm-thick E glasswoven cloth was impregnated and coated with the diluted varnish. The Eglass woven cloth was dried by heating at 165° C. for 3 min, to producea prepreg having a resin content of 50% by mass.

Production of Metal Foil-Clad Laminate

The obtained four or eight prepregs were stacked respectively, and 12μm-thick electrolysis copper foils were disposed on both upper and lowersides of the stack respectively. The copper foils and the stack werelaminate-molded (pressure-molded) by using a pressing machine underconditions of a planar pressure of 30 kgf/cm², a temperature of 220° C.,and a time of 120 min, to produce a metal foil-clad laminate having a0.4 mm-thick insulating layer and a metal foil-clad laminate having a0.8 mm-thick insulating layer.

Water absorption, insulation resistance, glass transition temperature,heat resistance after moisture absorption, and solder heat resistancewere measured and evaluated for the obtained metal foil-clad laminates.Results are shown in Table 1.

<Measurement Methods>

Measurement methods and evaluation methods of test methods are asfollows.

1) Water Absorption: the metal foil-clad laminate having a 0.4 mm-thickinsulating layer was cut into a size of 30 mm×30 mm×0.4 mm with a dicingsaw, and the copper foil formed on the surface was then left to obtain asample. Water absorptions after treatment for 1, 3, and 5 hours weremeasured for the sample under conditions of a temperature of 121° C. andan atmosphere of 2 atm in a pressure cooker tester (PC-3 typemanufactured by Hirayama Manufacturing Corporation) based on JIS C6481.

2) Insulation Resistance: the metal foil-clad laminate having a 0.4mm-thick insulating layer was cut into a size of 40 mm×20 mm×0.4 mm witha dicing saw, and the copper foil formed on the whole surface was thenremoved by etching to remove the whole copper foil on the surface,thereby obtaining a sample. Insulation resistances after treatment for1000 hours and non-treatment (treatment for 0 hours) were measured forthe sample under conditions of a temperature of 121° C. and anatmosphere of 2 atm in a pressure cooker tester (PC-3 type manufacturedby Hirayama Manufacturing Corporation) based on JIS C6481.

3) Glass Transition Temperature: the metal foil-clad laminate having a0.8 mm-thick insulating layer was cut into a size of 40 mm×20 mm×0.4 mmwith a dicing saw to obtain a sample. The glass transition temperaturewas measured for the sample with a dynamic viscoelasticity analyzer(manufactured by TA Instruments) based on JIS C6481.

4) Insulation Resistance Holding Rate: a value obtained by dividing avalue obtained by subtracting a value of insulation resistance aftertreatment for 1000 hours from a value of insulation resistance aftertreatment for 0 hours measured in the above (2) by the value of theinsulation resistance after the treatment for 1000 hours was representedby %.

5) Heat resistance after moisture absorption: the metal foil-cladlaminate having a 0.4 mm-thick insulating layer was cut into a size of50 mm×50 mm×0.4 mm with a dicing saw, and the whole copper foil otherthan a half part of one side was then removed by etching to leave a halfpart of the copper foil only on one side, thereby obtaining a testpiece. The test piece was processed for 3, 4, and 5 hours underconditions of a temperature of 121° C. and an atmosphere of 2 atm in apressure cooker tester (PC-3 type manufactured by Hirayama ManufacturingCorporation). The test piece was then immersed in a soldering vessel of260° C. for 60 sec, and the change in appearance of the test piece wasthen visually observed (the occurrence number of swellings/the number oftests).

6) Solder Heat Resistance: the metal foil-clad laminate having a 0.4mm-thick insulating layer was cut into a size of 50 mm×50 mm×0.4 mm witha dicing saw, and the copper foil formed on the surface was left toobtain a measuring sample. The change in appearance of the measuringsample was then visually observed in a state where the measuring samplewas floated in a soldering vessel of 280° C. for 30 min, and a timeuntil delamination occurred was measured. The notation “>30 min” inTable 1 means that the delamination does not occur even if 30 minpasses.

Comparative Example 1

A prepreg and a metal foil-clad laminate were produced in the samemanner as in Example 1 except that 42 parts by mass of a naphtholaralkyl phenolic resin (SN495V manufactured by Nippon Steel ChemicalCo., Ltd., hydroxyl equivalent: 236 g/eq.) instead of 58 parts by massof the naphthol-modified dimethylnaphthalene formaldehyde resin, 58parts by mass of a biphenylaralkyl-based epoxy resin (NC-3000-FH), and0.07 part by mass of imidazole (2E4MZ) were used, and a prepreg wasdried at 165° C. for 9 min when the prepreg was produced.

Various measurements and evaluations were performed in the same manneras in Example 1 using the obtained metal foil-clad laminate. Results areshown in Table 1.

Comparative Example 2

A prepreg and a metal foil-clad laminate were produced in the samemanner as in Example 1 except that 42 parts by mass of a biphenylaralkylphenolic resin (KAYAHARD GPH-103 manufactured by Nippon Kayaku Co.,Ltd., hydroxyl equivalent: 231 g/eq.) instead of 58 parts by mass of thenaphthol-modified dimethylnaphthalene formaldehyde resin, 58 parts bymass of a biphenylaralkyl-based epoxy resin (NC-3000-FH), and 0.04 partby mass of imidazole (2E4MZ) were used, and a prepreg was dried at 165°C. for 4 min when the prepreg was produced.

Various measurements and evaluations were performed in the same manneras in Example 1 by using the obtained metal foil-clad laminate. Resultsare shown in Table 1.

TABLE 1 Compar- Compar- Example ative ative 1 Example 1 Example 2 WaterAfter treatment 0.10 0.14 0.15 absorption (%) for 1 hour After treatment0.17 0.22 0.22 for 3 hours After treatment 0.19 0.25 0.25 for 5 hoursInsulation After treatment 2.6 × 10¹³ 5.4 × 10¹⁴ 1.1 × 10¹⁵ resistance(Ω) for 0 hours After treatment 1.8 × 10¹² 1.9 × 10¹¹ 5.2 × 10¹² for1000 hours Insulation resistance holding rate 6.92 0.04 0.47 (%) Glasstransition temperature (° C.) 171 186 167 Heat resistance Aftertreatment 0/4 0/4 0/4 after moisture for 3 hours absorption Aftertreatment 0/4 0/4 0/4 for 4 hours After treatment 0/4 0/4 0/4 for 5hours Solder heat resistance >30 >30 >30

As seen clear from Table 1, it was confirmed that Comparative Examples 1and 2 have water absorption higher than that of Example 1 and insulationresistance of Comparative Examples 1 and 2 remarkably lowered from anevaluation initial value. On the other hand, it was found that Example 1has an absorption rate significantly lower than those of ComparativeExamples 1 and 2 and an insulation resistance holding rate significantlyhigher than those of Comparative Examples 1 and 2 although glasstransition temperature, and heat resistance represented by heatresistance after moisture absorption, solder heat resistance and thelike of Example 1 are equivalent to those of Comparative Examples 1 and2. From the above, it is suggested that Example 1 has stability andreliability remarkably higher than those of Comparative Examples 1 and2.

As described above, the present invention is not limited to theabove-mentioned embodiment and Examples, and modifications can beproperly made in a scope that does not depart from the gist of thepresent invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention can be widely and effectivelyutilized in various applications such as electrical and electronicmaterials, a machine tool material, and an aviation material whichrequire a low absorption rate and high insulation stability.Particularly, the present invention can be effectively utilized insubstrate applications such as a printed wiring board and a laminatewhich require a low absorption rate, high insulation stability, andexcellent heat resistance.

The present application claims priority from Japanese Patent Application(Japanese Patent Application No. 2011-072637) filed to the Japan PatentOffice on Mar. 29, 2011, the contents of which are hereby incorporatedby reference.

The invention claimed is:
 1. A prepreg obtained by impregnating orcoating a base material (D) with a resin composition comprising: anaphthol-modified dimethylnaphthalene formaldehyde resin (A) having ahydroxyl equivalent of 300 to 600 n/eq.; an epoxy resin (B) having anepoxy equivalent of 250 to 350 g/eq.; and an inorganic filler (C),wherein the naphthol-modified dimethylnaphthalene formaldehyde resin (A)is obtained by condensing a dimethylnaphthalene formaldehyde resin and(c) a naphthol compound represented by the following general formula (1)in the presence of an acidic catalyst,

wherein R₁ and R₂ each independently represent a hydrogen atom or analkyl group having 1 to 3 carbon atoms, and the dimethylnaphthaleneformaldehyde resin is obtained by condensing (a) at least onedimethylnaphthalene selected from the group consisting of1,5-dimethylnaphthalene, 1,6-dimethylnaphthalene,2,6-dimethylnaphthalene, 1,7-dimethylnaphthalene,1,8-dimethylnaphthalene, and 2,7-dimethylnaphthalene and (b)formaldehyde in the presence of an acidic catalyst, the epoxy resin (B)is represented by the following formula (2):

wherein n represents an integer of 1 or more, the inorganic filler (C)is silica, a content of the naphthol-modified dimethylnaphthaleneformaldehyde resin (A) is 40 to 70 parts by mass based on 100 parts bymass in total of the naphthol-modified dimethylnaphthalene formaldehyderesin (A) and the epoxy resin (B), a content of the epoxy resin (B) is30 to 60 parts by mass based on 100 parts by mass in total of thenaphthol-modified dimethylnaphthalene formaldehyde resin (A) and theepoxy resin (B), and a content of the inorganic filler (C) is 5 to 300parts by mass based on 100 parts by mass in total of thenaphthol-modified dimethylnaphthalene formaldehyde resin (A) and theepoxy resin (B).
 2. A metal foil-clad laminate using the prepregaccording to claim
 1. 3. A printed wiring board using the metalfoil-clad laminate according to claim 2.